Hey, I really liked your game. The art and the music are very nice. The levels started out easy, but when you understand the game mechanics you have to start thinking more about the puzzles, which is good.
In some levels you can walk through some walls. For example in level 7 to the right of the middle door.
If you have time, you can also check out my game: https://lars-gielen.itch.io/recube